(a) Field of the Invention
The present invention relates to a negative active material for a rechargeable lithium battery, and a rechargeable lithium battery including the same.
(b) Description of the Related Art
Rechargeable lithium batteries use materials that are capable of reversibly intercalating or deintercalating lithium ions in positive and negative electrodes, and include an organic electrolyte solution or a polymer electrolyte between the positive and negative electrodes. Rechargeable lithium batteries generate electrical energy by an oxidation/reduction reaction during the intercalation/deintercalation of lithium ions at the positive and negative electrodes.
For a positive active material, composite metal oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), and LiMnO2, have been researched.
Conventionally, lithium metals have been used as a negative active material for a rechargeable lithium battery. However, an explosion can be caused by a short circuit of the battery due to formation of dendrites when using the lithium metal. Therefore, carbonaceous materials, such as amorphous carbon, and crystalline carbon, have recently been used as the negative active material in place of lithium metals. However, such carbonaceous materials impart a non-reversible capacity of 5 to 30% during the first several cycles, which wastes lithium ions and prevents at least one active material from being fully charged and discharged. Therefore, it has a disadvantage in its energy density.
In addition, it has recently become known that a metal negative active material such as Si, Sn, and so on, which is supposed to have a high capacity, has a problem in that it imparts non-reversible capacity characteristics. Further, the tin oxide disclosed by Japan Fuji Film. Co., Ltd. has come into the spotlight as an alternative to the carbonaceous material negative active material. However, the metal negative active material shows 30% or less initial Coulomb efficiency. Further, as lithium is continuously intercalated and deintercalated to generate a lithium-metal alloy, the capacity is remarkably decreased and the capacity preserving rate is remarkably deteriorated after repeating 150 charge and discharge cycles so that it cannot be commercially viable. Accordingly, much research has recently been undertaken to improve these characteristics.